Increasing environmental restrictions on logging and diminishing supplies of high quality old growth timber have led to dramatic escalation in the cost of lumber. In particular, clear lumber, i.e., lumber that is free of knots or other defects, has become especially valuable. Because of the increasing cost of natural clear lumber, it is desirable to provide a substitute product formed from lower cost raw material such as low grade lumber, i.e., lumber with knots, cracks or other defects. It is also desirable to recover useful lumber from the short pieces of lumber that are offal from various lumber processing operations and which would otherwise go to waste.
One way to create a long piece of clear lumber is to join small clear pieces together, usually with a joint called a finger joint. This is accomplished by taking short clear blocks from longer pieces of low grade lumber or offal and joining those blocks together. The use of finger joints in the assembly of the composite board results in a product that has nearly the same strength as a naturally occurring clear board. This allows lumber that is otherwise only suitable for low value uses to be converted to high value clear lumber.
Small pieces or blocks of wood are normally joined together with the aid of a finger jointing machine. The finger jointing machine mills or cuts fingers into each end of the blocks, applies glue to one or both ends and presses the blocks together so that the fingers on each block interlock, thus forming the final product. Most typically, the blocks are carried through the finger jointing machine on a conveyor that has a number of spaced apart lugs. The boards are placed in a spaced apart side-by-side arrangement, one in front of each lug, and the lugs carry or push the boards through the machine.
It is important that the finger jointing machine be capable of working with blocks of varying length to obtain the highest recovery of clear product from low grade source lumber. Existing finger jointing machines can typically mill and press together blocks ranging from 4" in length up to blocks 36" or longer. To avoid the additional step of sorting the short clear blocks into groups of uniform length, the machines are designed to accommodate blocks of assorted lengths in random order, within the above range. Thus, a 4" block may directly follow a 30" block, which may in turn be followed by a 16" block. Generally a single sequence of blocks will have the same thickness and width, but a finger jointing machine can usually be set to accept various thicknesses or widths of blocks by some adjustment or modification.
Unfortunately, although existing automated finger jointers are effective for carrying out the process of finger jointing, they are so complex and expensive as to preclude their use in smaller facilities with lower production requirements. As a result, many wood working facilities which might have a need for recycling a limited supply of short wood blocks have been unable to justify the substantial cost of existing automated finger jointers.